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Life Processes in Plants

NCERT Class 7 · Science Based on NCERT Class 7 Science textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explores how plants grow, obtain food, transport materials, and respire. It builds on the idea that all living beings need food and energy, but plants do not eat like animals—they make their own food. The one big idea a student must walk away with is that plants perform photosynthesis to produce food using sunlight, water, carbon dioxide, and chlorophyll, and they also respire to release energy for growth.
Key Concepts (12)
Photosynthesis
The process by which plants prepare food in the presence of sunlight and chlorophyll using carbon dioxide and water to produce glucose and oxygen.
e.g. A mango tree uses sunlight, water from the soil, and carbon dioxide from the air to make food in its leaves.
Chlorophyll
A green pigment present in leaves that helps in capturing sunlight efficiently for photosynthesis.
e.g. The green colour of a curry leaf or a tulsi leaf is due to chlorophyll.
Stomata
Tiny pores present on the surface of leaves that help in the exchange of gases like carbon dioxide and oxygen.
e.g. The tiny openings on the underside of a rhoeo leaf are stomata.
Xylem
Thin tube-like structures in plants that transport water and minerals from roots to all parts of the plant.
e.g. When a white sadabahar stem is placed in red ink, the red colour moves up through the xylem.
Phloem
Thin tube-like structures in plants that transport food (glucose/starch) from leaves to all other parts of the plant.
e.g. The sweetness in a potato comes from food transported through phloem from the leaves.
Respiration
The process by which glucose is broken down in the presence of oxygen to release carbon dioxide, water, and energy.
e.g. Germinating moong bean seeds in a flask produce carbon dioxide, which turns lime water milky.
Starch
A type of carbohydrate in which plants store food, detected by iodine test (turns blue-black).
e.g. A potato slice turns blue-black when iodine is added, showing starch is present.
Glucose
A simple carbohydrate produced during photosynthesis that serves as an instant source of energy and is later converted into starch for storage.
e.g. The food made in a leaf during photosynthesis is first glucose, then stored as starch.
Iodine test
A test to check the presence of starch; if starch is present, the leaf or substance turns blue-black.
e.g. In the activity, a decolourised leaf turned blue-black after adding iodine, confirming starch was made.
Destarching
Keeping a plant in the dark for two to three days to allow it to use up any stored starch.
e.g. Before the carbon dioxide experiment, the potted plant was kept in the dark to destarch it.
Caustic soda (sodium hydroxide)
A strong chemical that absorbs carbon dioxide from the air, used in experiments to show that carbon dioxide is essential for photosynthesis.
e.g. In the activity, caustic soda inside the bottle absorbed CO₂, so the leaf part inside did not make starch.
Vrikshayurveda
An ancient Indian text that records useful observations about plant growth, soil, and agricultural practices.
e.g. It describes methods of organic manure preparation using water, barley, and various seeds.
How It Works
Photosynthesis
  1. Leaves take in carbon dioxide from the air through stomata.
  2. Roots absorb water and minerals from the soil, which travel up through xylem to the leaves.
  3. Chlorophyll in the leaves captures sunlight energy.
  4. Using sunlight energy, carbon dioxide and water are converted into glucose and oxygen.
  5. Glucose is used for energy or converted into starch for storage.
  6. Oxygen is released into the air through stomata.
💡 Students often forget that oxygen is released during photosynthesis, not carbon dioxide. Also, photosynthesis happens only in the presence of sunlight and chlorophyll.
Respiration in Plants
  1. Glucose (from food) is broken down in the presence of oxygen.
  2. This process releases carbon dioxide, water, and energy.
  3. The energy is used by the plant for growth and development.
  4. All parts of a plant—green or non-green—carry out respiration.
💡 Respiration occurs all the time (day and night), while photosynthesis only occurs in sunlight. Students often confuse the two processes.
Transport of Water and Minerals (Xylem)
  1. Roots absorb water and dissolved minerals from the soil.
  2. Water and minerals enter the xylem vessels in the roots.
  3. Through xylem, water and minerals move upward to the stem, leaves, and other parts.
  4. This water is used in photosynthesis and other functions.
💡 Xylem transports only water and minerals upward; it does not transport food. The red ink experiment shows this clearly.
Transport of Food (Phloem)
  1. Leaves produce food (glucose/starch) during photosynthesis.
  2. Food is loaded into phloem tubes in the leaves.
  3. Phloem transports food to all parts of the plant—roots, stems, fruits, seeds.
  4. Food may be stored in roots (e.g., carrot), stems (e.g., potato), or seeds.
💡 Phloem transports food in both directions (up and down), unlike xylem which only goes upward.
Starch Test (Iodine Test)
  1. Boil a leaf in water for five minutes to soften it.
  2. Dip the leaf in alcohol (in a test tube placed in boiling water) until it becomes colourless.
  3. Place the decolourised leaf on a plate.
  4. Add a few drops of diluted iodine solution on the leaf.
  5. If the leaf turns blue-black, starch is present.
💡 The leaf must be decolourised first so that the colour change from iodine is visible. Alcohol is flammable—never heat it directly.
Experiment to Show Carbon Dioxide is Essential for Photosynthesis
  1. Destarch a potted plant by keeping it in the dark for 2-3 days.
  2. Place caustic soda (absorbs CO₂) in a wide-mouthed bottle.
  3. Insert half of a destarched leaf into the bottle through a split cork, leaving the other half outside.
  4. Place the set-up in sunlight for a few hours.
  5. Remove the leaf and test for starch using iodine.
  6. The part outside the bottle turns blue-black (starch present), the part inside does not (no CO₂).
💡 Caustic soda is a strong chemical that can cause burns—only teachers should handle it. The experiment proves CO₂ is necessary for photosynthesis.
Exam Traps — Don't Make These Mistakes
⚠ Confusing photosynthesis and respiration
✗ Photosynthesis releases carbon dioxide and respiration releases oxygen.
→ It is the opposite: photosynthesis uses carbon dioxide and releases oxygen; respiration uses oxygen and releases carbon dioxide.
✓ Photosynthesis: carbon dioxide + water → glucose + oxygen (in sunlight). Respiration: glucose + oxygen → carbon dioxide + water + energy.
⚠ Thinking only leaves respire
✗ Only green leaves respire because they have chlorophyll.
→ All parts of a plant—roots, stems, leaves, seeds—respire. Respiration is a life process in every living cell, not just green parts.
✓ All parts of a plant, green or non-green, carry out respiration to release energy.
⚠ Mixing up xylem and phloem functions
✗ Xylem transports food and phloem transports water.
→ Xylem transports water and minerals upward from roots; phloem transports food from leaves to all parts.
✓ Xylem: water and minerals from roots upward. Phloem: food from leaves to all parts.
⚠ Forgetting that oxygen is a product of photosynthesis
✗ Photosynthesis produces only glucose.
→ Photosynthesis produces both glucose and oxygen. Oxygen is released into the air.
✓ During photosynthesis, plants produce glucose and release oxygen.
⚠ Thinking starch is the first product of photosynthesis
✗ Starch is the first food made in photosynthesis.
→ Glucose is the first product; it is then converted into starch for storage.
✓ Photosynthesis first produces glucose, which is later converted into starch for storage.
Compare & Contrast
Overall process
Photosynthesis
Respiration
Photosynthesis makes food using sunlight, CO₂, and water; respiration breaks down food to release energy.
Substance transported
Xylem
Phloem
Xylem transports water and minerals upward; phloem transports food (glucose/starch) in all directions.
Location and function
Stomata
Leaf surface
Stomata are tiny pores (mostly on lower surface) for gas exchange; the leaf surface is broad and flat to capture sunlight efficiently.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 Very Short Answer (1 mark), 1 Short Answer (3 marks), 1 Long Answer (5 marks) — total approximately 10 marks
Most asked: Photosynthesis: definition, word equation, raw materials, products · Role of chlorophyll, sunlight, water, and carbon dioxide in photosynthesis · Starch test (iodine test) and its interpretation · Difference between xylem and phloem · Respiration in plants: word equation and comparison with photosynthesis · Stomata: location and function
Don't skip: Word equation of photosynthesis and respiration (often 3 marks); Explain an experiment to show that carbon dioxide is essential for photosynthesis (5 marks); Compare and contrast xylem and phloem (3 marks); Describe the starch test on a leaf (3 marks)
One-Line Revision (read aloud before the exam)
  1. Photosynthesis is the process by which plants make food using sunlight, water, carbon dioxide, and chlorophyll.
  2. The word equation for photosynthesis is: Carbon dioxide + Water → Glucose + Oxygen (in sunlight, with chlorophyll).
  3. Leaves are called the 'food factories' of plants because they produce food.
  4. Chlorophyll is the green pigment that captures sunlight for photosynthesis.
  5. Stomata are tiny pores on leaves that allow exchange of carbon dioxide and oxygen.
  6. Xylem transports water and minerals from roots upward to all parts of the plant.
  7. Phloem transports food (glucose/starch) from leaves to all other parts of the plant.
  8. Respiration in plants: Glucose + Oxygen → Carbon dioxide + Water + Energy.
  9. All parts of a plant respire, not just leaves.
  10. The iodine test turns blue-black in the presence of starch.
  11. Destarching means keeping a plant in the dark to use up stored starch before an experiment.
  12. Caustic soda absorbs carbon dioxide and is used to show that CO₂ is needed for photosynthesis.
  13. During photosynthesis, oxygen is released; during respiration, carbon dioxide is released.
  14. Glucose is the first product of photosynthesis; it is stored as starch.
  15. Plants need both sunlight and water for growth, as shown by the pot experiment.

MCQs — 10 Questions with Answers

Q1. In Activity 10.1, which pot had the best plant growth after two weeks?

  • A. Pot A (sunlight with water) ✓
  • B. Pot B (sunlight without water)
  • C. Pot C (dark with water)
  • D. All pots grew equally

Answer: A — Pot A had both sunlight and water, which are essential for plant growth, while Pot B lacked water and Pot C lacked sunlight.

Q2. What is chlorophyll?

  • A. A type of starch stored in leaves
  • B. A green pigment that captures sunlight ✓
  • C. A nutrient absorbed from soil by roots
  • D. A gas present in the air

Answer: B — Chlorophyll is the green pigment in leaves that helps capture sunlight energy for photosynthesis.

Q3. When iodine is added to a leaf containing starch, what colour appears?

  • A. Yellow
  • B. Red
  • C. Blue-black ✓
  • D. Green

Answer: C — Iodine solution turns blue-black when it reacts with starch, indicating starch is present.

Q4. Which gas from the air is essential for plants to prepare food?

  • A. Oxygen
  • B. Nitrogen
  • C. Carbon dioxide ✓
  • D. Hydrogen

Answer: C — Carbon dioxide from the air is one of the three essential ingredients for photosynthesis in leaves.

Q5. In Activity 10.3, why did the non-green patches of the leaf NOT turn blue-black with iodine?

  • A. Because they were in sunlight
  • B. Because they lacked chlorophyll needed to make starch ✓
  • C. Because water could not reach them
  • D. Because they were exposed to carbon dioxide

Answer: B — Non-green patches have little or no chlorophyll, so they cannot produce starch even with sunlight, water, and CO₂.

Q6. A student noticed that the leaves of her indoor plant turned yellow. Based on the chapter, what is the most likely reason?

  • A. The plant was watered too much
  • B. The plant lacked sufficient sunlight to produce chlorophyll and starch ✓
  • C. The soil had too much nitrogen
  • D. The room temperature was too low

Answer: B — Indoor plants away from sunlight cannot produce enough chlorophyll, which makes leaves yellow and reduces starch formation.

Q7. A farmer wants to increase crop production in his field. Which of the following should he ensure?

  • A. Crops are kept in shade to prevent wilting
  • B. Fields are watered regularly and have maximum sunlight exposure ✓
  • C. Soil is completely dry to concentrate nutrients
  • D. Fields are covered with plastic sheets

Answer: B — Regular watering and maximum sunlight exposure provide both water and light needed for photosynthesis and food production.

Q8. In Activity 10.4, the part of the leaf inside the bottle with caustic soda did not produce starch because:

  • A. It was away from sunlight
  • B. It did not have chlorophyll
  • C. The caustic soda removed carbon dioxide from the air around that leaf part ✓
  • D. The leaf part inside was not green

Answer: C — Caustic soda absorbs carbon dioxide, and without CO₂, leaves cannot synthesize starch even with sunlight, water, and chlorophyll.

Q9. A greenhouse farmer keeps plants in a closed room with artificial lighting but without ventilation holes. Why would his plants eventually show poor growth?

  • A. Artificial light is not as strong as sunlight
  • B. Carbon dioxide levels would decrease inside the closed room, limiting starch production ✓
  • C. The roots would not get enough water
  • D. Chlorophyll would break down in artificial light

Answer: B — Without ventilation, plants consume CO₂ faster than it is replenished, reducing the raw material available for photosynthesis.

Q10. In an experiment, one leaf was kept in bright sunlight for 6 hours and another identical leaf in complete darkness for 6 hours. After iodine testing, which leaf would show more blue-black colour?

  • A. The leaf in darkness because chlorophyll is more active there
  • B. The leaf in sunlight because photosynthesis produced more starch ✓
  • C. Both would show equal blue-black colour
  • D. Neither leaf would show any blue-black colour

Answer: B — Sunlight drives photosynthesis, so the leaf in bright sunlight produces more starch, resulting in a stronger blue-black colour with iodine.

Flashcards

What is the green pigment in leaves that helps capture sunlight?

Chlorophyll is the green pigment that helps leaves capture sunlight energy for food production.

Why are plant leaves called 'food factories'?

Leaves are called food factories because they produce starch (food) using sunlight, water, and carbon dioxide.

What colour does iodine turn when starch is present?

Iodine turns blue-black in colour when starch is present in a leaf.

Name three things a plant needs to make starch.

Plants need sunlight, water, and carbon dioxide from the air to make starch.

Why did the plant in Pot B (sunlight, no water) die in Activity 10.1?

The plant died because without water, it could not transport nutrients or perform photosynthesis, even with sunlight.

In Activity 10.4, why did caustic soda prevent starch formation in half the leaf?

Caustic soda absorbed carbon dioxide from the air, and without CO₂, the leaf part inside the bottle could not make starch.

What does destarching a plant mean?

Destarching means keeping a plant in darkness for 2-3 days so it uses up all stored starch before an experiment.

Why do non-green patches of a leaf not show blue-black colour in an iodine test?

Non-green patches lack sufficient chlorophyll to produce enough starch that can be detected by iodine.

Which two factors were most important in making Pot A plants grow fastest?

Sunlight and water were the two most important factors that made Pot A plants grow fastest.

Why must alcohol never be placed directly near a heat source during the starch test?

Alcohol is highly flammable and can easily catch fire and cause burns if placed near heat.

Important Board Questions

What is the role of chlorophyll in plant leaves? [1 mark]

Chlorophyll captures sunlight energy and helps produce starch. Focus on 'green pigment' and 'sunlight capture'.

Based on Activity 10.1, explain why Pot A plants grew better than Pot C plants even though both had water. [2 marks]

Pot A had sunlight (photosynthesis could occur) while Pot C was in darkness (no starch production). Mention both factors.

Describe the experiment (Activity 10.2) you would perform to test for the presence of starch in a leaf. What colour change indicates the presence of starch? [3 marks]

Steps: boil leaf in water, dip in alcohol to decolourize, place on plate, add iodine drops. Blue-black colour = starch present. Include why decolourization is needed.

Design an experiment to prove that all three factors — sunlight, water, and carbon dioxide — are essential for photosynthesis in plants. Describe the experimental setup, observations, and conclusions for each factor. [5 marks]

Draw three pots: (1) sunlight + water + CO₂ = starch forms, (2) sunlight + water, no CO₂ = no starch, (3) no sunlight + water + CO₂ = no starch. Include iodine test results and label diagrams showing each variable.

Assertion-Reason Questions for Life Processes in Plants

Q1. Assertion (A):

Plants require both water and sunlight for healthy growth and development.

Reason (R):

Water is essential for various metabolic processes, and sunlight is necessary for photosynthesis and starch production in leaves.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true. Activity 10.1 proved that Pot A with both factors showed best growth, and Activity 10.3 showed sunlight is essential for starch production. The reason correctly explains why both factors are necessary, making this answer 'A'.

Q2. Assertion (A):

Chlorophyll is the green pigment that helps leaves capture sunlight efficiently.

Reason (R):

Without chlorophyll, plants cannot perform respiration and obtain energy for growth.

Answer: B — Both A and R are true, but R is NOT the correct explanation of A — The assertion is true; chlorophyll does capture sunlight. However, the reason is incorrect. Chlorophyll's role relates to photosynthesis, not respiration. While both are true statements, the reason does not correctly explain why chlorophyll captures sunlight. Answer 'B' fits this pattern.

Q3. Assertion (A):

Starch is produced only in the green parts of a leaf when exposed to sunlight.

Reason (R):

Non-green parts of leaves lack chlorophyll, which is necessary for photosynthesis and starch production.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true. Activity 10.3 showed that only green patches produced starch (blue-black color), while non-green patches did not. The reason correctly explains why non-green parts cannot produce starch — absence of chlorophyll. Answer 'A' is correct.

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Case-Based Questions (CBQ) for Life Processes in Plants

Case Study:

Meera conducted a science fair project investigating plant growth. She grew four identical tomato seedlings in similar soil and pots. She kept Plant 1 in bright sunlight with daily watering, Plant 2 in bright sunlight but watered only once a week, Plant 3 in indirect light with daily watering, and Plant 4 in complete darkness with daily watering. After 3 weeks, she measured plant height and recorded the number of leaves. Plant 1 was the tallest with vibrant green leaves. Plant 2 showed stunted growth and drooping leaves. Plant 3 had moderate growth with pale green leaves. Plant 4 appeared extremely weak with yellowish leaves. She then performed an iodine test on leaves from each plant and recorded the results in a table showing starch presence.

Q1. Based on Meera's observations, which factor appears to be the most critical for plant growth?

  • A. Indirect light is better than direct sunlight
  • B. Regular watering and adequate sunlight are both essential for healthy growth ✓
  • C. Darkness promotes leaf coloration and growth
  • D. Once-weekly watering is sufficient for tomato plant growth

Answer: B

Q2. In Meera's experiment, Plant 3 showed pale green leaves despite having regular water. What is the most likely explanation?

  • A. Indirect light limits chlorophyll production, resulting in pale coloration ✓
  • B. The soil quality for Plant 3 was deficient in nutrients
  • C. Pale color indicates the plant was developing starch faster
  • D. Plant 3 received too much water despite daily watering

Answer: A

Q3. If Meera performed an iodine test on leaves from all four plants, which result would she most likely observe?

  • A. Plant 1 would show blue-black color; Plant 4 would show no color change ✓
  • B. All plants would show blue-black color because all had water
  • C. Plant 4 would show the strongest blue-black color due to darkness
  • D. Plant 2 would show darker blue-black than Plant 1 due to stress

Answer: A

Q4. What conclusion can Meera draw about the relationship between light and starch production based on her experiment?

  • A. Starch production is independent of light availability
  • B. Light exposure is necessary for starch production and plant growth ✓
  • C. Only indirect light can trigger starch production in leaves
  • D. Watering frequency affects starch production more than light does

Answer: B

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